The use of softening and strengthening agents in the manufacture of tissues, such as facial and bath tissue, is common practice in the industry. These tissues typically contain a blend of relatively long fibers, which are usually softwood fibers, and relatively short fibers, which are usually hardwood fibers. The softening and strengthening agents may be separately added to these different fiber species prior to or after blending the fibers together and forming the tissue web. Preferably, the softening agent is added to the short fibers since the short fibers primarily contribute to tissue softness. The long fibers are separately treated with strengthening agents (wet and dry) and refining. Both refining and strengthening agents are used because excessive use of either treatment may have an adverse effect on the tissue making process and/or the resulting tissue product. In particular, temporary wet strength resins are often added to tissue products to impart integrity to the tissue when wet. For bath tissue, sufficient wet strength is required to minimize "feathering" after flushing and maintain integrity during use. Feathering, which is the phenomena of retaining residual fragments of tissue left in the toilet bowl after flushing, is perceived as undesirable by consumers from both an aesthetic and strength viewpoint. However, the wet strength resin also needs to be temporary, meaning it disintegrates over time in the presence of water to prevent plugging of sewer systems and septic tanks.
However, the conventional method of adding temporary wet strength agents to the fiber furnish has some disadvantages. This adds additional expense (chemical delivery system, material cost) and requires constant monitoring to maintain wet tensile specification. Also, temporary wet strength resins invariably have a relatively short shelf life due to their propensity to cross-link and subsequently gelling making it difficult to handle in a mill environment. Variations in temperature and humidity can exacerbate this phenomena.
Therefore there is a need for a more efficient method of utilizing temporary wet strengthening agents in the manufacture of tissues.